Method of attd means eob protecting



Nov. 6, 1928. 1,690,271

L. M. CLEMENT METHOD OF AND MEANS FOR PROTECTING ELECTRICAL APPARATUS Filed Nov. 12, 1923 9 f 2- 3 4 J/ J 8, 6 i 20 Z E /4 g m /5 Z4\ Z6 26 W e/var dew/3M. 676/7760) Patented Nov. 6, 1928.

UNITED .srrss PATENT or ice.

LEWIS M. CLEMENT, OF YONKERS, NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED; OF NEW YORK, N. Y.', A

conr oRA'rIoN-cr' NEW'IYORK METHOD or AND MEANS FOR PROTECTING-ELECTRICAL A'ZPP-ARATUS.

Application filed November 12,1922. Serial in 674,159. 7

Tliisduveution relates to'a IDQi-lIOd Of and means for protecting-;elcc-trical apparatus from the el'i'ectsof an abnormal flow oficurrent in a circuitincludihgthe apparatus.

This invention contemplates an arrange ment for automatically increasingthe;nesist+ ance of; a circuit-and therebydecreasing the current- 7 so that the a current a flowing. .in; the circuit is maintained at a' predeterminedflow value until the cause of the abnormajhcendition has vbeenlocatedyand: propergprecau-i.

tionstaken'to insure against its recurrence when the circuits are restored-tor normal operatingconditionsigf Three electrode -discharge i devices have been ap lie tl very extensively in var-iousarts, particu arlyin the communication art, with a tendency toward-the employment of; larger andrmore. costly-devices of this ty pc,-;par ticularly for-oscillators, amplifiers,-,- modulators and radio I telephone ,.and jtelegr aph transmitters= Undercertain conditions, Y if the discharge-devices fail to operate forthc purpose intended; an excessivecurncnt'may be set up in the circuits associatedqwith them and in tliedevices themselves which may be thereby destroyed or rendered'valueless in a very short time. f In accordance with one feature of the present invention, the automatic'controlof' the resistance of the circuit is accomplished-by controlling the conductivity ofthe space cub rent pat-h existing between thecathode and anode of an electric discharge-device, in -response to abnormal current conditions either in a circuit of the device or in another circuit. It is a well-known characteristic of electric disch arge devices having three electrodes thatthe space current orcatho'de anodecurrent is dependent upon theirelativepotent-ials of the cathode and the control electrode orgrid. If the control electrode'i's made suificiently negative with respectto the cathod eQthe space current is reduced to zero and the effective resistance of the path between the cathode and the anode approaches infinity. By fixing definitely the relative potentials of the -cathode and control electrodegthe devicemayhe used to prevent the transmission of a current of more than a predeterminedvalue through a circuit in which it is included The present inveutionprovides an arrangement which is responsive to abnormal current flow in the circuit to be protected for automatically fixing the relative potentials of the cathodeand control electrodes of -a discharge device included. ingsaid circuitjtoiltherpby limit .the curreut, flowing through this circuit to a predetermined vsate value. W-liile the; arrangement capable of. quite general appl cation, is particularly, adapted Efor usezgxvrtlr, disch arge devices, i vhj erleby such devices lnay he rendered self-protecting. a Form d stan n efthe p e nt nan; tron and the operation of; its various .p reference may'be had totheffolloiviiig descrips tion .takengin connection lvvithtthe iattached dra-wing,.i,;n WhichEig. lshowsthe invention applied ,toa simple vacuum tube circuit-of general application; and Eig. .2 as applied to a radio signal transmitting circuit. In Fig.1; thereis shoWn an electric discharge device comprising acontainer l, en-. closing. a cathode, 2, a. control electrode or grid-3 and anauode t. Heatiugzcurrentfis supplied togcathode aby a-g'sou'rcea. 4 ,i a is vyyell known: when the (iathode has been heated, if the grid 3 .is not :more nc g aftivc,v than the filament. aspace current Will flow between-it-he;.cathode and anodeiqand through the external;- circuit connected Qto these 1 electrodes. v {This ci-rcuitqis :commonly referred to as the plate or; outputcircuit of the device. :In: the presentinstancmthe plate circuit ,may be traced from the positive side of a suitable source of current 7, the..actuating or,c ontrol Winding of a circuithi'eaker 8, the primary inding; of the transformer 9, the plate 4', the cathode 2 andthecontacts of the circuit'breaker 8 to the negative terminal of the source 7. The input circuit of the device extends from the cathode 2 to the grid 3. This circuit includes the contacts of the circuit breaker 8 and secondary winding of the transformer 10. 1

In I the normal operation of the device, changes in potential which maybe induced in the secondary of the inputtransformer 10 due to the operation of an instrument such as a telephone transmitter or a telegraph ikey connected, to the primary thereof, are impressed-upon the control electrode or'grid3 and cause the current in-the output circuit of the device'to vary in-accordance withthe variations of potential impressed upon the grid. These variations maybe utilized in,a circuit including the secondary of the trans former9.

The contacts o'f'the circuit breaker'8 form a shunt about ;a resistance-ll whichl-"isi-con ncctedlbetween *tlie filameiit' and 'thelnegative side of the source 7. The resistance" 11 is therefore included in a conductive path which uea o t0 be h the inp t nd Output i cuits o fvthedevice dr --,The ;cir c u it breaker 8 is adjusted to open its contacts in response to the flow of circuiti-in excess of a predetermined value in the plate circuit. It follows, therefore, that, if for-any reason, current in the plate circuit exceeds the predetermined value, the circuit'brea'ker 8'lwill operate to remove the shunt about the resistaiie'e ll. As soon as the shunt circuit is opened, the grid 3 will be directly connected tothe negative terminal of the source 7 whilethe cathode 2 will connectto this termi'nal through there sistance "11?! Platecurrenfiwill therefore new through the resistance 1'1, and hence the rid 3 will bem'ore' negative mam-theatre 'e 2 bylthe dropj ef potential across this resistance. The resistance *11is 'so'chosen'th at the poten tial difference, thereby"i'nril iressed'fupon the grid, will be sufii'cient toreduce the current flow betweent-he-cathode and plate either to zeroor to some safe predetermined jvalue.

In Fig. 2, there is "sho'wjn a radio sigma 'sys-- tem comprising a modulator 1'1 andan-oscillator 15. The modulator and oscillator are herein shown by way of examplejas electric discharge device's, each comprising a container'enclosing a cathode,agri'd ,or control electrode and an anode] 'fThe' modw lator 14' and the oscillator '15 ,-1mve; their plates connected together'by a condu'ctor 16 which is connected to acommon plate supply source'17 through a'cho'ke'coil 18. 2' f The choke coil 18 is so; chosen that the total current supplied by the source 17 to the parallel connected space paths of the oscillator and modulator is maintained substantially constant.v i Low frequency signaling: or modulating currents flowing through, the circuit 12 are impressed upon the input circuit of the modulator 14 to produce in its output circuit a signal modulated direct current which is sup plied to the plate circuit of the oscillator to generate modulated carrier waves. By this arrangement, a carrier wave modulated in amplitude in accordance with the low frequency signaling currents is generated and radiated from the antenna 19.

The arrangement for producing modulated carrier waves described'above is similar to'thatdisclosed in U. S. Patent 1,442,147, January 16,1922 to R. A.- Heising, to which reference may be made for a complete'description of its operation. i p

The plate circuit of the oscillator 15 may be traced from' the positive terminalof the source 1fl' choke coil 18,"conductor 16, inductance 20, across'the space between'thc plate and cathode to the oscillator 15, contacts of the circuit breaker 21 and conductor 22 to the negative terminal of the source 17.

The input circuit ofrtheloscillator'inay be traced from'the cathode, contacts of the circuit breaker 21, conductor 23, a leak path comprising the resistance 2 1 and control or actuating coil-:25 oithe circuit breaker 21 connected in series and a condenser connected in parallel tocthe resistance--24 and coil 25, inductance 27 to the grid of the oscillator.

The input and'oiit-put circuits of the oscillator are coupled in feed-back relation by the inductance 28 which'is inducti'vely'associated with the inductances 20 and 27. The inductance 28 is included in the antenna circuit 1-9 which, in genera-l, serves to'deterniine the frequency of'the carrier waves generated by theoscillator15. A static leak path is included in'the-a'ntenna' circuit. "This path comprises a'series connected resistance 29 and condenser 30, and is connected-in shunt to the coil 28.

A resistance 31lfis'connecte'd between the cathode of the oscillator'lfiand'the common terminal of -the"'conductors'22 and 23,- and ience is included in a' conductive path common' to the in'p'ut'and-output circuits of the oscillator15.' I In the normal operation of the system de scribed above,-theresistance 31 will be shunted by the contacts of'thecircuit breaker 21. However,"should an abnormal potential of positive sign be ixnpres'sed-upon the gri'd of t-he'oseillato'r, as for'exainple, when the circuit' ceases to oscillate, current will flow through theinputcircuit of the oscillator including' the actuating'coil 25 oi'the circuit breaker 21. By adjusting'the'circuit breaker so that it will operate when the aniplitude-of the current flowing throughthei'gr-id circuit reaches a selected value the relative-values of the potentials respectively impressed upon the grid and anode of the oscillating device 1.5 may befixed. The impression of a positive potential upon the grid ofithe' oscillating device in "excess 'of the selected value would cause the amplitude of'the current flowing through the plate circuit of the device 15 and hence between its cathode and anode, to increase" b yond a predetermined value which may be safely transmitted across .the space within the device;

When the grid of the oscillating device 15 is positively polarized beyond the selected value, the circuit breaker 21:will-be operated to-remove the shunt around the resistance 31, and this resistance will be included in the conductive path'common to the input and out-put circuits of the oscillator. \Vhenthis occurs, the negative terminal of'the source 17 will be connected to the grid ofthe'oscillator. through the leak resistance '24 and the cathode of the oscillator will be connected to the negative terminal of the'source-l'lithrough the resistance 31. Space current will flow through the resistance 31 to-setup a difierence of'potential across this resistance; The gridofthe I ll! for using the .device 'topredetermine the value tion .of the oscillating vented.

f rangements describedabove,

oscillator will therefore be more negative than its cathode by the voltage drop across the terminals of the resistance 31. Y

By selecting a resistance 31 of such value that the potential difference between its terminals is relatively large, the current discharged across the space Within the oscillatiug device 15 will be reduced either to zero or to a safe value, whereby damage to or-destrucdevice will be pre- From the preceding description, it will be apparent that this invention provides an arrangement for automatically rendering an electric discharge device self-protecting and of the current which may besupplied to electricalapparatus.

While the inventiondhasibeen herein de scribed. with reference to signaling, for the purpose of completely and clearly disclosing its nature, itwill be appreciated that this invention maybe applied generally to a rrange-- me'ntszfor predetermining' the maximum amplitude of the current'which may be supplied to electrical-apparatus, and heneemay be used inany circuit where this effect is desired, such as, for example, in power circuits.-

' including an electric discharge device and its amociated input and output circuits having acommon portion, whichscomprises utilizing an effect produced. by the' flow-olfabnormal current in one ofsaid c'ireuits-zto initiate the supply of current to said common portion, whereby the relative ,potent-ials impressed upon the electrodes of the device are'regulated and the currentsupplied to the apparatus is limited toa safe value. H

2. The methodof protecting electrical apparatus from abnormal current flow ina'cire cuit including a space discharge device hav ing a cathode, an anode and an impedance control element and input and output circuits havinga common portion associated with the device, which comprises causing the flow of abnormal current in one of said circuitsto initiate the supply of current to said common portion, whereby the relative potentials impressed upon the anode and control electrode are varied to reduce the space current flowing through he device to a safe value.

3. The method of protecting electrical apparatus from abnormal currents in a circuit including a space discharge device and associated input and output circuits having a common portion, said device having a cathode an anode, an impedance control electrode ut onl y by the which comprises causing excessive current flow through one of. said-circuits to initiate thesupply ofj current to..said common portion, wherebyawpolarizing? potential is im: pressed upon ,the' control electrode :to reduce the current discharged ac-ross'the space within said device to a safe limit. .1 L-

-4. The method of protecting'eleetricaliapparatus from 'abnormal currentsina circuit. including a space discharge device and assog ciated. input a'ndout-putcircuits, havingwacommon portion, said. device having ,a cathode, an'anode, an impedance controlelec' trode which comprises causingv eurrent to', flow ina circuit includingthe-spaoepa'th be tween the anode.- and-.cathodeeand causing abnormal change said current-to; initiate.

the supply of current to said conunon portion,- i-uhereby a-ipolanizimg potntialiis impressed uponlthe r control electrode of: the; device-to ren dent-he} spate :path substantially ILOllr-COIl'l ducti've:

.5.- Protective means for an ielectric' circuit.

including :an electric discharge device, input and output circuitsxtherefor; having: a com.- mon;portioi1,said devioefhaving a-cathodmnananode and a 'gridca'nd meansdncluded in Zone of said r circuits, for initiating; .the; supply; of

current to said common portionfwhereby'"; the.

space current of'sa-id device is prevented from exceeding a'prqdeterminedvalue. r

"6. Protective means for an electric circuit including an electric discharge device com? prising acath0de,-an anode,-a gr1d, .and input and output circuits for 'sa1d-dev1ce,'a circuit breaker included in oneofisaid circuits, and

means controlled by said circuit breaker for preventing the. space current of said device from exceeding a predetermined value.

7. Protective meansfor an electriccircuit including an electric-discharge device comprising a cathode, an anode, a grid, and input and output circuits for said device, and a circuit breaker. having its contacts in said circuits and actuated by current in one of said circuits for controllingm'eans to prevent the space current flowing through said device from exceeding a predetermined value.

8. In combination, a circuit to be protected, including a space discharge .device having three electrodes and external circuit-s associated therewith, means common to said external circuits for controlling the relative values of the potentials impressed upon two of the electrodes oi said device, and means controlled by current flow in one of said circuits for supplying current to said common means for limiting the space current flowing through said device to a safe value.

9. In combination, a circuit to be protected, including a space discharge device having an anode, a cathode, an impedance control electrode and external circuits associated therewith, means common to said external circuits for controlling the relative values of the potentials impressed upon said anode and said control electrode, and means controlled by current flowing in the circuit including said anode and cathode for supplying current to said common means controlling the potentials for limiting the space current through said device to a safe value.

10. In combination, a circuit to be protected, including a space discharge device having an anode, a cathode, an impedance control electrode and external circuits associated therewith, and a circuit breaker included in said external circuits for controlling means whereby the relative value of the potentials impressed upon said anode and said control electrode is changed to limit the space current flowing through the device to a safe value. 1

11. In combination, a circuit to be protected including a space discharge device having an anode, a cathode and an impedance control electrode and external circuits associated'therewith, and a circuit breaker adapted to be-actuated by abnormalcurrent flowing in'one of said external circuits for controlling means whereby theimpedanee of the space discharge path is increased and the space current flowing through-the device is reduced to a safe value. I

n12. In'combination, a'circuit to be protected including a space discharge path and input and: output" circuits associated therewith,

means for controlling the impedance of said iischar'ge path, and means sensitive to the flow of excessive current in one of said external circuits forsupplying current to the means for controlling the said impedance of said device to limit the space current to a safe value.

13. Protective means for a circuit including an electric discharge device having a cathode, an anode and a grid, input and output circuits associated with said device, said output circuit including a space current source, a resistance included in a conductive path common to said input and output circuits, and means under the. control of one of said circuits for renderng said common path conductive of space cur rent, whereby the space current for said de vice is prevented from exceeding a predetermined value. I

14. Protective means for a circuit including an electric discharge device having a cathode, an anode and a grid, input and output circuits associated with said device, said output circuit includinga space current source,-a resistance including in a conductive path common to said input and output circuits, and means under thecontrol of one of-said circuits for rendering said common. :path conductive of space current and-to impress the potential difference across said resistance upon the control electrode of said device. a

15. Protective means for a circuit including an electric discharge device having. a cathode an anode and a grid, input and output circuits associated with-said device, said output circuit: including -a "space current source, a resistanceincluded-ina conductive path common-to said input and outpnt-:.'cir-= cuits, and a circuitbreaker,-controllegl by one of said circiiits,'-for supplying space' current to said resistance, whereby the-current charged across the space within. saididevi ce is prevented from I exceeding a predetermined value.-' i'ii; 3 i. in i2.

16. Protective means for a circuit including anelectric discharge device havingacathode, an anode and 'a'i grid, input and :qutp'nt -circuits associated with'said devioe,.said output circuit including a space'zcurrent-sourc'e, a resistance included in a conductivepath common t-osaid input androutputcircuits, and a circuit breaker, controlledby-one'o'f said cir-i. cuits, for supplying spa'c'e .currentto Esaidresistance and for impressing the-potential dropv across said resistance" upon' the grid of-:saiddevice. i 1

17 A self-protectingapparatus. comprising an electric discharge device including a cathode, an anode, agrid,and'inputzandioiitput' circuits therefor and nieans:adapted.to beenergized by the-flowof abnormalgcurrent-in one of said circuits for controllingmeans com-- mon to said circuits for impressing-a block- 1g potential upon said grid. 7

18. A self-protecting apparatus comprising an electric discharge device including a cathode, an anode, a-grid, and input and output circuits therefor, and a circuit breaker =adapt-- ed to be energized by the flow'of abnormal current in one ofsaid circuits for controlling means common to said circuits for impressing a blocking potential upon said grid.

In witness whereof, I hereunto subscribe my name this 5th day of November -A. D., 19:23.

LEWIS M. CLEMENT. 

